1. Field of the Invention
The present invention relates to an ultraviolet curing inkjet printer in which a head ejecting ultraviolet curable ink scans a plurality of times for each single line on a recording medium, a printing method used in the ultraviolet curing inkjet printer, and a head.
2. Discussion of the Background
Conventionally, in case of printing on a transparent medium (recording medium) such as a polycarbonate film by an ultraviolet curing inkjet printer, a backing process is conducted. That is, after a color image are printed with color ultraviolet curable inks (UV ink: Ultraviolet ink) to form an image layer on the medium, a white UV ink is superposed on an upper layer (surface) of the color image to form a ground color layer in order to show the color printed image vibrantly. Therefore, the head of the conventional UV inkjet printer is provided with an imaging inkjet head and a backing inkjet head which is disposed anterior to the imaging inkjet head in the feeding direction (for example, see JP-A-2007-050555). The head is further provided with ultraviolet emitting devices for emitting ultraviolet light, which are disposed posterior to the imaging inkjet head and the backing inkjet head in the scanning direction, respectively. The contents of JP-A-2007-050555 are herein incorporated by reference in their entirety.
UV inks are ejected from the imaging inkjet head and ultraviolet light is emitted from a UVLED while the head is moved in the scanning direction, a color image is printed. Then, after the medium is moved in the feeding direction, the head is moved in the scanning direction again, a white UV ink is ejected from the backing inkjet head, and ultraviolet light is emitted from a UVLED, thereby backing the color image with the white UV ink.
For the purpose of improving the print quality, there has been devised a multipass printing method in which UV inks are superposed by scanning a plurality of times for each single line. However, the conventional ultraviolet curing inkjet printer has a problem that UV ink is finally cured at every scanning so that the UV inFk on the upper layer side (outer side) is liable to be stripped because it is rejected by the UV ink on the lower layer side (media side).